The present invention relates to a radar apparatus for measuring a range, rate and azimuth angle of an object by transmitting an electromagnetic wave and receiving the wave reflected from the object.
A conventional radar system for automobiles transmits an electromagnetic wave such as light and a radio wave and receives the signal reflected from an object such as an automobile and an obstacle. A transmission time required for an electromagnetic wave to reach an object and return to the radar system, an intensity of the reflected signal, a Doppler shift frequency and the like are detected from the reflected signal to measure a range (distance), rate (relative speed) and azimuth angle of the object. The application field of a radar system is broad. A radar apparatus for automobiles has been developed recently which is mounted on an automobile to measure a range to a front vehicle. A radar apparatus is also applied to the field of home security systems as one kind of electromagnetic sensing means.
A radar apparatus utilizing a laser beam generally adopts a pulse method by which measures the range of an object from a travelling time required for a pulsed laser beam to reach the object and return to the apparatus. There are several methods for a radar apparatus utilizing a radio wave to measure a range and rate of an object. Known methods include: a two-frequency continuous wave (CW) method which switches two frequencies in a time duplex manner; a frequency modulated continuous wave (FMCW) method which performs triangular modulation of a transmission frequency; a pulse modulation method which measures the range of an object from a travelling time required for a pulsed wave to reach the object and return to the apparatus; and other methods. With the two-frequency CW method and FMCW method, a received signal is subjected to a fast Fourier transform (FFT) process and the range and rate of an object are measured from the frequency, phase and amplitude information of a peak signal in a frequency spectrum obtained by FFT.
An electric power for driving such a radar apparatus for automobiles is required to be generated in each vehicle. As described, for example, in JP-A-08-136646, power consumption is reduced by operating, at different timings, high frequency electronic equipment such as an oscillator and a modulator of a radar apparatus utilizing a radio wave.
With such a conventional method, however, although the consumption power can be reduced, the area to be covered by a radar apparatus is searched in a time division manner so that there is a possibility that some objects may not be detected.